Light generating device having polarized light emitting waveguide plate

ABSTRACT

The present invention relates to a light generating device comprising a slab light guide ( 1 ), at least one light input unit ( 2 ) arranged on at least one side ( 10 ) of said light guide ( 1 ) comprising at least one light source ( 20 ) and a light incoupling means ( 21 ) for coupling light into said light guide ( 1 ), and at least one light output unit ( 3 ) arranged on at least one side ( 11 ) of said light guide ( 1 ). In order to provide a device that provides polarized light of a high homogeneity the light output unit ( 3 ) according to the present invention comprises a polarized light emitting waveguide plate ( 31 ) for selectively coupling light of a first polarization state out of said light guide ( 1 ). 
     The present invention further relates to a display device, in particular an LCD, comprising a light generating device according to the invention.

The present invention relates to a light generating device comprising aslab light guide, a light input unit and a light output unit. Further,the present invention relates to a display device and an LCD televisionset.

Currently used slab light guides, such as those used for theback-illumination of thin LC display screens, are typically of theedge-lit (also called side-lit) type where a light source, partiallysurrounded by a reflector, is positioned adjacent to at least one of theedges of the light guide such that its light is directed into the lightguide via its edges. Such a slab light guide is, for instance, disclosedin WO 01/63588 A1. Light captured in the light guide propagates throughthe light guide via total internal reflections (TIR) and is normallycoupled out of the light guide and directed away from the light guidevia optical interactions of the propagating light inside the light guidewith light scattering and/or reflecting/refracting means such asscattering dots, scattering surface patterns, or other optical“irregularities” provided to the light guide surfaces, or via speciallyproduced topographies in/on the light guide surfaces, all lightscattering and/or reflecting/refracting means having in common that they“frustrate” the total internal reflections and induce light outcouplingfrom the light guide. Alternatively, specially textured optical foilsmay be brought into optical contact with the light guide for the purposeof light outcoupling and its subsequent directing. With such a set-up itis possible that the entire edge-lit backlight can be contained within aspace having only a small thickness, which is important for applicationsinvolving i.e. thin notebook screens or thin LC monitor screens.

A polarized light emitting waveguide plate for anisotropicallyscattering light having a particular polarization state, for instances-polarized light, out of a light guide, which is preferably used in aliquid crystal display, is described in WO 01/90637 (PHNL 000294 EPP).Said waveguide plate comprises an entrance side for coupling light intothe waveguide plate, a major exit surface for coupling light out of thewaveguide plate and polarization means for selectively directing acomponent of a first polarization state of light coupled in via theentrance side towards the exit surface, the polarization meanscomprising an anisotropically light scattering layer which selectivelyscatters the component of the first polarization state towards the exitsurface. Thus, light recycling in a light guide is used to make anLCD-panel more efficient. The idea is to reflect p-polarized light atthe surface of an anisotropic foil while s-polarized light is scatteredout of the light guide. The p-polarized light can be recycled asdepolarisation occurs in the light guide.

However, using such a waveguide plate, light recycling and extraction ofs-polarized light is too efficient. It has been found thatdepolarisation can occur at a distance of just a few millimeters, thusgiving rise to loss of homogeneity in the light flux. A few centimetersaway from the light source most of the light is already extractedresulting in a decrease of intensity.

It is therefore an object of the present invention to provide a lightgenerating device which overcomes the above described problems, which inparticular generates polarised light having a high homogeneity and issuitable for use in an LCD panel of the backlighting type.

This object is achieved according to the present invention by a lightgenerating device as claimed in claim 1 comprising

a slab light guide having two substantially parallel sides and at leastone edge, the edge having a surface connecting the surfaces of saidsides,

at least one light input unit arranged on at least one side of saidlight guide comprising at least one light source and a light incouplingmeans for coupling light into said light guide, and

at least one light output unit arranged on at least one side of saidlight guide comprising a polarized light emitting waveguide plate forselectively coupling light of a first polarization state out of saidlight guide.

The present invention is based on the idea to provide at least one lightinput unit and at least one light output unit which, dependent on theapplication and contrary to the known devices, can be arranged anywhereat any position on at least one side of said light guide. This enablesthe light guide to act as a light buffer between the light input andlight output units which are not directly optically coupled to eachother. Light buffering inside the light guide promotes light intensityhomogenisation to be attained across the surface area of the at leastone side of the light guide covered by the at least one light outputunit, which is advantageous for obtaining outcoupled light of a ratheruniform lateral brightness level. The indirect degree of couplingbetween the light input and light output units via the light guide has aproportionality to their respective areas of optical contact with thelight guide, i.e. to their apertures, and additionally depends on thepositioning of the respective light input units and light output unitson at least one side of the said light guide with respect to each other.

According to the invention a polarized light emitting waveguide platefor selectively coupling light of a preferred polarization state out ofthe light guide is provided in the light output unit. Thus, only thelight with the preferred polarization state, e.g. s-polarized light,will be extracted out of the light guide, thus achieving efficientpolarized light recycling without loss of homogeneity. Further, thefabrication of such a light generating device is quite easy. The lightgenerating device according to the invention is preferably used in anLCD display device of the direct back-lighting type or an LCD televisionset with scanning back light which is a known option to reduce motionartefacts in LCD television sets.

The number of light sources, e.g. lamps, used in the light input unitscan be scaled with the side area of the light guide and can thus be madeto scale with a display screen surface area that must be illuminated orwith the surface area of a light-emitting luminaire tile. This allowslight generating devices to be created that, dependent on the details oftheir design, enable a high degree of lateral brightness uniformity tobe attained at high brightness levels pertaining to the emitted lightfrom the at least one light output unit arranged on at least one side ofsaid light guide, or enable light concentration or light dilution to beaccomplished. Furthermore, dependent on the design parameters of the atleast one light output unit, light can be emitted from the lightgenerating device that possesses a certain degree of collimation. Thisis useful, e.g. for illuminating a LCD screen positioned directlyadjacent to the at least one light output unit.

Preferred embodiments of the invention are defined in the dependentclaims. A display device, in particular a liquid crystal display deviceof the direct back-lighting type, comprising a display screen, inparticular a LCD screen, and a light generating device according to theinvention is claimed in claim 14. A LCD television set comprising alight generating device according to the invention is claimed in claim15.

In the context of the invention, a polarized light emitting waveguide isa waveguide which selectively emits light of a first polarization statewith respect to light of a second polarization state orthogonal to saidfirst polarization state. The polarization selectivity of the emittedlight is defined as the ratio of the emitted amount of light of a firstpolarization state to the emitted amount of light of a secondpolarization state orthogonal to said first polarization state. Thetransmissivity of the waveguide plate is the ratio of the amount oflight emitted via the exit surface to the amount of light entered viathe entrance side.

The incident light coupled in via the entrance side of the waveguideplate is guided through the plate by total internal reflection indirections more or less parallel to the exit surface. Generally, thisincident light is substantially unpolarized, that is to say, it containscomponents of the first and the second polarization state in equalamounts. As this light travels through the anisotropically scatteringlayer, the component of the first polarization state is scattered to alarger extent than the component of the second polarization state.

Conversely, the component of the second polarization state istransmitted to a larger extent than the first component, that is to say,the second component is selectively transmitted and hence remainscaptured in the waveguide plate. Scattered light traveling towards theexit surface and incident on the exit surface at an angle not satisfyingthe condition for total internal reflection will be refracted and exitthe waveguide plate via the exit surface.

The thickness of the waveguide plate is attuned to the amount of lightneeded for a particular application at hand and the size of the lightsource used to provide light to the waveguide plate. If the plate is toothin, the spreading of the light is less efficient, whereas if it is toothick weight is added unnecessarily. Conveniently, the thickness isbetween 0.1 and 50 mm, or better 0.25 to 20 mm. A good balance betweenefficient spreading and weight of the plate is struck at a thickness of0.5 mm to 10 mm.

In order to efficiently illuminate a display panel of an LCD devicecomprising the waveguide plate in accordance with the invention, thetransmissivity of the waveguide plate with respect to the component ofthe first polarization state (that is the component to be coupled outvia the exit surface) in the direction of waveguiding may be selectedsuch that any light which reaches the side opposite from the entranceside comprises to some extent said component of the first polarization.

Preferred embodiments of the anisotropically light scattering layerwhich can be applied in the light generating device according to thepresent invention are disclosed in the above mentioned WO 01/90637 (PHNL000294 EPP), which disclosure is herein incorporated by reference.

In an alternative embodiment, the waveguide plate of the output unitcomprises a micro-structured anisotropic light outcoupling layerproviding mainly the same effect as the above-described anisotropicallylight scattering layer. In addition, a protective coating can beprovided on top of said anisotropic layer on the side facing away fromthe light guide. Preferred embodiments of the micro-structuredanisotropic light outcoupling layer are defined in claim 4.

In an advantageous embodiment, the waveguide plate comprises a hologramoutcoupling layer as described in European Patent application011206666.1 (PHNL010683). Therein the Bragg angle is preferably 90° orthe thickness of the hologram outcoupling layer is chosen such thatoutcoupling is polarization-selective.

In another embodiment of the invention a reflective polarizer andoutcoupling structure, as for instance described in U.S. Pat. No.5,808,713, is provided which is preferably a broad band cholestericnetwork, a multilayer film or a wire grid polarizer.

The light incoupling means of the light input units preferably comprisesa plurality of incoupling optical elements being in optical contact withthe surface of the side of said light guide on which the at least onelight input unit is arranged. Such incoupling optical elements can be inthe form of ribs or cubes or cylinders possessing a round or oval crosssection, having different sections and surfaces, as defined further inclaims 10 to 14.

According to an advantageous embodiment, the light guide is providedwith light reflection means, in particular a specular or diffusereflector, at its edge, the diffuse reflector being substantially not inoptical contact with the light guide. Thus, the light rays will beforced to propagate through the light guide via TIR until they exit thelight guide either via the light input unit or via the light outputunit. An additional reflecting surface is preferably positioned behindand/or around the at least one light source in the at least one lightinput unit, that is, in the direction away from the light incouplingmeans, to redirect light rays propagating away from the light incouplingmeans back towards the light incoupling means. The presence of the saidadditional reflecting surface allows light recycling to be accomplishedwithin the light input unit.

Preferably, for use as a homogeneously light-emitting back-lighting unitfor a large-area LC display screen, the light input unit is spreadacross the whole surface area of the side of the light guide on which itis arranged. Further, individual light sources can be regularlypositioned along this side within the light input unit. Similarly, thelight output unit can be spread across the whole surface area of theside of the light guide on which the light output unit is arranged.

The invention will now be explain in more detail with reference to thedrawings in which

FIG. 1 shows a first embodiment of a light generating device having ananisotropically light scattering layer,

FIG. 2 shows a second embodiment of a light generating device having amicrostructured anisotropic layer,

FIG. 3 shows a third embodiment of the light generating device havingabsorption means for absorbing non-TIR light rays,

FIG. 4 shows a liquid crystal display device according to the invention,

FIG. 5 shows a fourth embodiment of a light generating device having amicrostructured anisotropic layer,

FIG. 6 shows a sixth embodiment of a light generating device having aholographic outcoupling layer, and

FIG. 7 shows a seventh embodiment of the light generating device havinga reflective polarizer.

FIG. 1 shows a first embodiment of a light generating device accordingto the present invention. Said device comprises a slab light guide 1, alight input unit 2 arranged on one side of the light guide 1 and a lightoutput unit 3 arranged on another side of the light guide 1. The lightguide 1 has two substantially parallel sides 10, 11 and an edge 12 whichhas a surface connecting the surfaces of the sides 10, 11. The lightinput section 2 covers the entire side 10 of the light guide 1; thelight output section 3 covers the entire side 11 of the light guide 1.

Within the light input unit 2 five lamps 20 are provided at equalintervals for generating light. For incoupling the generated light intothe light guide 1 the light input unit 2 further comprises lightincoupling means 21 comprising a plurality of incoupling opticalelements 22 in the form of ribs or cubes or upstanding cylinders ofround or oval cross section in optical contact with the flat light guidesurface 10. The upstanding surfaces 23 of the optical elements 22aligned substantially perpendicularly to the light guide surface 10 areoptically smooth and serve to couple light 41 from the light input unit2 into the interior of the light guide 1. The surfaces 24 of the opticalelements 22 aligned parallel to the light guide surface 10 are coveredwith a reflecting layer, preferably made of aluminium and having areflectivity of substantially 100%, to prevent any light entering thelight guide 1 that cannot propagate through the light guide 1 by TIR.Preferably, the surfaces 24 of the optical elements 22 are diffuselyreflective at the side of said surfaces 24 facing away from the lightguide 1 to reflect light 42 within the light input unit 2.

The light input unit 2 including the light sources 20 is at least partlysurrounded by a diffuse reflector 27, except of course when the sun oran external light source shall be used as a light source for generatinglight 4 to be coupled into the light guide 1. Said diffuse reflector 27preferably has a reflectivity of 100% to maximize the lumen output andlight recycling efficiency within the light input unit 2.

Captured light rays propagate through the light guide 1 via TIR. Theymay exit either via the upstanding walls 23 of the incoupling opticalelements 22 of the light incoupling means 21, which brings them back inthe cavity of the light input unit 2 containing the light sources 20from where they can be recycled and again coupled into the light guide1, or they may exit through the waveguide plate 31 of the light outputunit 3.

The waveguide plate 31 has an entrance side 32 for coupling in light anda major exit surface 33 for coupling out polarized light. The waveguideplate 31 comprises polarization means for selectively directing acomponent of a first polarization state of light coupled in via theentrance side 32 towards the exit surface 33 in the form of ananisotropically light scattering layer which selectively scatters thecomponent of the first polarization state towards the exit surface 33.The layer comprises, in a preferred embodiment, a continuous phase 34 inwhich a disperse phase 35 is dispersed. The refractive indices of thecontinuous and the disperse phase are attuned to one another such thatalong a first axis orthogonal to the direction of waveguiding (normal tothe entrance side 32) the refractive index of the disperse phase and thecontinuous phase are substantially mismatched, whereas along a secondaxis orthogonal to both the direction of waveguiding and said first axisthe refractive indices are substantially matched. Alternatively, thefirst axis may be oriented parallel to the normal to the entrance side32 or the normal to the exit surface 33.

The waveguide plate 32 can be developed further and can be provided withadditional elements, such as, for instance, a reflector for redirectingany scattered light incident thereon towards the exit surface 33, areflector 12 for redirecting any light transmitted by the waveguideplate into a waveguide plate and/or a dichroic polarizer arrangedbetween the waveguide plate 31 and an external display panel to furtherenhance the polarization selectivity. In this regard, reference is againmade to WO 01/90637 describing further embodiments of a waveguide platewhich can generally all be used in the light generating device accordingto the present invention.

Typical trajectories of polarization components of light rays travelingthrough the light guide 1 and the waveguide plate 31 are also shown inFIG. 1. A light ray 51 of unpolarized light comprising equal amounts ofs-and p-polarized light enters the waveguide plate 31 via the entranceside 32. While traveling through the continuous phase 34 of theanisotropically light scattering layer 31, it encounters a dispersephase area 35. The refractive index of the disperse phase 35 forp-polarized light is substantially matched to that of the continuousphase 34 of the anisotropically light scattering layer 31 and thus thep-polarized component is substantially transmitted. The refractive indexof the disperse phase 35 for s-polarized light is mismatched with thatof the continuous phase 35. The mismatch results in scattering of theincoming light ray 51 into a bundle of scattered light rays 61, 62 atleast a fraction of which, i.e. light ray 61 being s-polarized, isdirected towards the exit surface 33. Polarization selection is thusobtained. Other light rays 62, being p-polarized, are scattered backinto the light guide 1 where they, as shown for light rays 52, arerecycled by total internal reflections, i.e. by specular reflections atreflecting surfaces 25, 13 and 14. Thus, efficient polarized lightrecycling is achieved without loss of homogeneity of the outcoupledlight 61.

The light generating device according to the present inventioncomprising a slab light guide, a light input unit and a light outputunit, enables the light guide 1 to act as a light buffer between theinput and output units 2, 3. These units 2, 3 are not directly opticallycoupled to each other, the (indirect) degree of optical coupling betweenthem has a proportionality with their apertures, i.e. their respectiveareas of optical contact with the light guide 1. The extent of lightbuffering between the light input unit 2 and light output unit 3possesses therefore an inverse proportionality to the aperture of boththe input and output units 2, 3. The (indirect) degree of opticalcoupling between the units 2,3 additionally depends on the positioningof the respective units 2,3 with respect to each other on the sides ofthe light guide 1.

At the edges 12 of the light guide 1, TIR light propagating into onedirection is back-reflected by means of a specular or, preferably,diffuse reflector 13, the latter preferably not being in optical contactwith the light guide 1. This enables an additional smoothing of thelight intensity across the light guide 1.

FIG. 2 shows another embodiment of a light generating device accordingto the present invention. Therein the light output unit 3 comprises,instead of the anisotropically light scattering layer shown in FIG. 1, amicro-structured anisotropic layer 37 covered from the outside by anoptional protective coating 36. The micro-structured anisotropic layer37 generally fulfils the same function as the anisotropically scatteringlayer 31 as described above, i.e. also with the embodiment shown in FIG.2 light of a particular state of polarization, e.g. s-polarized light,can be selectively and homogeneously emitted over the whole side 11 ofthe light guide 1.

S-polarized light that is scattered back towards the reflectors 24, 25of the light incoupling elements 21 may escape from the light guide 1even if depolarisation occurs. However, when applying the embodiments ofthe light generating device shown in FIGS. 1 and 2 in a liquid crystaldisplay, where the LCD panel is located below the light output unit 3,the LCD panel itself will select the s-polarization by its polars. Asmall loss of light will be the result, but the contrast is stillsufficiently good.

There is, however, the possibility to omit the first polar in the LCDpanel, thus making it cheaper in total, if only light withs-polarization can escape from the light guide 1. This can be achievedwhen light absorption means are provided to prevent non-TIR lightescaping the light guide 1 through the light output unit 3. This isillustrated in FIG. 3 showing a third embodiment of a light generatingdevice according to the invention. Therein the light output unit 3comprises an anisotropically polarized light scattering layer 31 asillustrated in FIG. 1. The light incoupling means, however, comprise,besides the adjacent optical elements 22 which are arranged at equalintervals along the side 10 of the light guide 1, a shaped foil or mask26 having a diffusely or specularly reflecting layer on the side facingthe light sources 20. This shielding foil 26 shields the light guidesurface between adjacent optical elements 22 from direct exposure to thelight generated by the light sources 20 and is preferably not in opticalcontact with the light guide 1 so that cavities 28 are formed betweenthe foil 26 and the light guide surface 10.

Further, the surface of the optical elements 22 and the shaped foil 26facing the light guide 1 is covered by an absorption layer 29, e.g. ablack coating, in order to absorb light rays 53 having a non-TIR angleso as to prevent non-TIR light from escaping the light guide 1. Thus, afull TIR mode is maintained so that one polar of an LCD device can beomitted.

FIG. 4 schematically shows, in a cross-sectional view, a liquid crystaldisplay device of the back-lighting type comprising a light generatingdevice in accordance with the invention. The LCD device 70 comprises anLCD panel 71 which, in general, includes an LC cell dispersed betweentransparent ITO electrodes. The device 70 further comprises a lightgenerating device as described above having a light input unit 2, alight guide 1 and a light output unit 3 including a waveguide plate forselectively directing polarized light to the exit surface 33. The LCDdevice 70 further comprises an analyzer/polarizer 72 arranged betweenthe viewer 80 and the panel 71.

The LCD device 120 is of the back-lighting type, thus being capable ofdisplaying picture information using light generated from the lightinput unit 2. As is well known in the art, depending on the particularLC cell used, mutual orientation of the analyzer 72 and the optionalpolarizer(s) enables different LC effects to be obtained. With novoltage on a pixel of the panel 71, polarized light emitted from thelight output unit 3 enters the panel 71. As it passes the LC cell thepolarization of the light is turned by 90° so that it cannot pass theanalyzer 72: the pixel appears dark. With the pixel in the ON state, thepolarization of the light is not changed in the panel 71 and thus thelight is able to pass the analyzer 72 unhindered: the pixel appearswhite.

Another embodiment of a light generating device according to the presentinvention is shown in FIG. 5, which is a combination of parts of theembodiments shown in FIGS. 2 and 3. The light incoupling structure 2 isadapted as shown in FIG. 2 using an array of ridges or prisms as lightincoupling means 21. The light guide 1 and the light output unit 3 isadapted as shown in FIG. 2, i.e. the light output unit 3 comprises amicro-structured anisotropic layer 37 for selectively outcouplings-polarized light. Thus a high control over the light emission directioncan be achieved with this embodiment.

FIG. 6 shows an embodiment of the light generating device according tothe present invention using a holographic outcoupling layer. While thelight input unit 2 and the light guide 1 are adapted as shown in FIG. 2,the light output unit 3 comprises, besides the optional protectivecoating 36, a hologram outcoupling layer 38. At the hologram, onepolarization of the incident light 51 is selectively coupled out ifeither the Bragg angle α is 45° or if the thickness of the layer 38 issuitably chosen. Thus light of s-polarization 61 is selectively coupledout.

FIG. 6 also shows the hologram tilt angle β, which is the angle betweenthe normal to the grating planes and the stacking direction, thestacking direction being the direction in which the grating planes arestacked. The hologram may be thought of as a stack of grating planes,the refractive index being constant within each grating plane anddifferent between adjacent planes. Regarding a more detailed descriptionof such a hologram layer 38 reference is made to the above mentionedEuropean patent application 01 120 366.1 (PHNL 010683). This embodimenthas the advantage of a simple outcoupling construction requiring nomicro-structuring and no Moire interference.

FIG. 7 shows still another embodiment of a light generating deviceaccording to the present invention. The light input unit 2 and the lightguide 1 are again adapted as shown in FIG. 2. The light output unit 3comprises, besides the optional protective coating 36, a reflectivepolarizer 39, which selects the light having a particular polarization.Thus, light having a particular polarization, e.g. s-polarization 61,can be selectively coupled out by an outcoupling layer 30. Light of adifferent polarization, e.g. p-polarization 62, is reflected on thereflective polarizer 39. This embodiment has the advantage of beingindependent of the outcoupling construction, e.g. different outcouplinglayers 30 can be used in this embodiment.

The present invention provides a light generating device in which thelight guide acts as a light buffer. Selectively polarized light of apreferred polarization state is emitted homogeneously. The layout of thedevice is simple, which can be used in a wide range of differentapplications.

1. A light generating device comprising: a slab light guide having twosubstantially parallel sides and at least one edge, the edge having asurface connecting the surfaces of said sides; at least one light inputunit arranged on at least one side of said light guide, the light inputhaving at least one light source and a light incoupling means forcoupling light into said light guide; at least one light output unitarranged on at least one side of said light guide comprising a polarizedlight emitting waveguide plate for selectively coupling light of a firstpolarization state out of said light guide, wherein said waveguide platecomprises a micro-structured anisotropically light outcoupling layer. 2.A light generating device as claimed in claim 1, wherein said lightincoupling means comprises a plurality of incoupling optical elementsbeing in optical contact with the surface of said at least one side ofsaid light guide, said incoupling optical elements having a reflectivesurface section facing the light source and being aligned substantiallyparallel to the surface of a side of said light guide and at least onetransparent surface section being arranged at an angle different from0°, in particular at an angle of substantially 90°, with respect to thesurface of a side of said light guide.
 3. A light generating device asclaimed in claim 2, wherein said incoupling optical elements arearranged at intervals and wherein between said incoupling opticalelements light reflecting means are arranged, in particular a structuredreflective foil or structured reflective mask that is substantially notin optical contact with said light guide and is reflective on the sidefacing the light source.
 4. A light generating device as claimed inclaim 2, wherein said incoupling optical elements and/or said lightreflecting means have a light absorbing surface section facing the lightguide.
 5. A light generating device as claimed in claim 2, wherein saidincoupling optical elements are arranged at intervals and whereinbetween said incoupling optical elements light reflecting means arearranged, in particular a reflective layer in optical contact with saidlight guide that is specularly reflective on the side facing the saidlight guide.
 6. A light generating device as claimed in claim 2, whereina reflective surface section of the said incoupling optical elements isdiffusely reflective having a reflectivity of substantially 100% at theside of said reflective surface section facing away from the lightguide.
 7. A light generating device as claimed in claim 1, wherein saidlight guide is provided with light reflection means in particular aspecular or diffuse reflector, at its edge.
 8. A light generating deviceas claimed in claim 1, wherein said waveguide plate comprises a hologramoutcoupling layer.
 9. A light generating device as claimed in claim 8,wherein the Bragg angle is substantially 45°.
 10. A light generatingdevice as claimed in claim 8, wherein the thickness is chosen such thatoutcoupling is polarization selective.
 11. A light generating device asclaimed in claim 1, further comprising a reflective polarizer andoutcoupling structure.
 12. A light generating device as claimed in claim11, wherein said reflective polarizer is a broad band cholestericnetwork, a multilayer film or a wire grid polarizer.
 13. A lightgenerating device as claimed in claim 1, wherein said micro-structuredanisotropically light outcoupling layer is a liquid crystalline polymeror a birefringent polymer, in particular PET or PEN.